1. Field of the Invention
The present invention relates to a heterocyclic compound, an organic light-emitting diode including the heterocyclic compound, and a flat panel display device including the organic light-emitting diode.
2. Description of the Related Art
Organic light-emitting diodes (OLEDs), which are self-emitting devices, have advantages such as a wide viewing angle, excellent contrast, quick response, high brightness, excellent driving voltage characteristics, and can provide multicolored images. Thus, OLEDs have drawing attention.
A general organic light-emitting diode has a structure including a substrate, and an anode, a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and a cathode which are sequentially stacked on the substrate. In this regard, the HTL, the EML, and the ETL are organic thin films formed of organic compounds. When a voltage is applied between the anode and the cathode, holes injected from the anode move to the EML via the HTL, and electrons injected from the cathode move to the EML via the ETL. The holes and electrons recombine in the EML to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted. In this regard, emission occurring when singlet excitons drop from an excited state to a ground state refers to “fluorescence”, and emission occurring when triplet excitons drop from an excited state to a ground state refers to “phosphorescence”. Since a probability of excited singlet exciton is 25% in the fluorescence, the light emitting efficiency is limited. However, 75% of excited triplet excitons and 25% of excited singlet excitons can be used in the phosphorescence, and thus internal quantum efficiency increases up to 100%.
U.S. Pat. Nos. 6,596,415 and 6,465,115 disclose an organic light-emitting diode using 4,4′-N,N-dicarbazole-biphenyl (CBP) as a host of an emission layer. CBP is a widly known host material of a phosphorescent emitting material, and an organic light-emitting diode with high emission efficiency of green and red colors and using phosphorescence is well known in the art. The organic light-emitting diode includes Ir(ppy)3, as a phosphorescent dye having a heavy element such as Ir and Pt with high spin-orbital coupling at its center, PtOEP, as a dopant, and CBP, as a host, so that light is efficiently emitted in a triplet state (phosphorescence). Recently, an iridium (III) complex has been known as a phosphorescent dopant material, and (acac)Ir(btp)2, Ir(ppy)3 and Firpic, and the like are well known in the art for RGB emission. In addition, an organic light-emitting diode including CBP as a host material of a phosphorescence emitting material, and BCP and Balq in a hole blocking layer is reported, and a high performance organic light-emitting diode using a BAlq derivative as a host is disclosed. However, the organic light-emitting diode has a short lifespan of 150 hours or less. This is because, CBP has a low glass transition temperature Tg of 110° C. or less, is easily crystallized, and has low thermal stability. Thus, CBP deforms during a high-temperature deposition.
International Publication No. WO2009/148015 discloses an organic light-emitting diode including a polycyclic compound as a host material. The polycyclic compound has a π-conjugated heteroacene backbone crosslinked with carbon atoms, nitrogen atoms, oxygen atom, or sulfur atoms, and is prepared by a synthesis of a halogen compound. An organic light-emitting diode including the polycyclic compound has high light emittin efficiency and long lifespan. However, these organic light-emitting diodes have sufficient electrical stability, and thus cannot be commercialized.